Anion which can react with $dil. H_2SO_4$ is

When salt $BA$ is treated with concentrated $H_2SO_4$, a reddish-brown gas is liberated. The aqueous solution of $BA$ gives a pale yellow precipitate with $AgNO_3$ solution. Which of the following anions $(A^-)$ is present in the salt $BA$?

$A$ substance reacts with dilute $H_2SO_4$ to release a colorless gas which $(i)$ turns baryta water turbid and $(ii)$ turns acidic dichromate solution green. This reaction indicates the presence of which of the following?

$A$ salt solution is treated with chloroform drops. Then it is shaken with chlorine water. The chloroform layer becomes violet. The solution contains:

$A$ white crystalline salt $A$ reacts with dilute $HCl$ to liberate a suffocating gas $B$ and also forms a yellow precipitate. The gas $B$ turns potassium dichromate acidified with dilute $H_{2}SO_{4}$ to a green coloured solution $C$. $A$,$B$ and $C$ are respectively

The brown ring test is used for the detection of which of the following?